Office equipment such as photocopiers, laser printers, ink jet printers and other imprinting mechanisms today incorporate an ability to store and supply sheet media from a stack. This stack is typically stored within the covers of the equipment or in a covered tray installed in the equipment. Such storing of a media stack not only enhances the overall aesthetic appeal of the equipment, but it also reduces exposure of mechanisms in the equipment to dust and foreign materials. The covered media stack is however invisible to a user. As such a user is unable to tell the status of the media stack without having to remove the covers. In many of the equipment, the only indication the user receives of a media-out status is a signal when the media supply has actually been exhausted. Normally, the signal is issued during a printing or copying job and requires the job to be interrupted to re-supply the media stack. It is preferable that a continuous indication be given of the current status of the media stack so that the user is able to interrupt the copying or print job at a convenient point to replenish the stack.
There are many existing mechanisms for indicating the status of a media stack in a media tray. These mechanisms usually rely on the position of a stack support for detecting and indicating the media stack status. One such mechanism is described in the U.S. Pat. No. 5,236,348. The stack support is positioned within a media tray. One end of the stack support is pivotably mounted to the tray housing. The other free end of the stack support is thus moveable about this pivot between a tray-empty position and a tray-full position. A spring support attached to a base of the stack support biases the free end of the stack support towards the tray-empty position. When a full stack of media is loaded into the tray, the stack support is pushed to a tray-full position. As media in the tray is consumed, the stack support is pushed towards the tray-empty position. A pivotably mounted indicator lever positioned within the tray cooperates with the stack support to indicate the media stack status. A first portion of the lever is in contact with a surface of the stack support such that as the stack support moves between the tray-empty and tray-full positions, a second portion of the indicator lever is moved accordingly to reflect the media stack status.
Though such a simple and cost-effective mechanism works well, it is heavily reliant on the peculiar operation of the stack support for deriving the media stack status. Not all equipment will employ such a stack support design. In such equipment, the mechanism described will not be suitable for the purpose of indicating a media stack status. A new mechanism will be required. One such equipment which requires the new mechanism is one which employs a stack support which moves up and down during each pick cycle. This stack support design is necessary to allow the equipment to use a single motor for driving a pick roller as well as a media feed. During a pick cycle, the stack support is moved towards the pick roller to allow a top sheet on the media stack to be drawn out of the tray roller into an infeed zone. Once the sheet is engaged by the pick roller, the stack support is moved away from the pick roller so that no new sheets are picked during a subsequent media feed cycle, where the picked sheet is transported to a print zone.
From the foregoing, the prior art has a need for a media stack status indicator which derives information for indicating the media stack status independently of a stack support.